1. Field of the Invention
The invention relates generally to surgical instruments. In particular, the invention relates to endoscopic instruments and, more particularly, to means for increasing the forces which are able to be exerted by a pair of scissor blades operating at the distal tip of an endoscopic instrument.
2. Description of the Prior Art
Scissors are an obviously well-known type of surgical instrument. With the recent interest in endoscopic surgery in which surgical procedures are performed through one or more cannulas inserted into the body, there has been a commensurate interest in developing endoscopic instruments--scissors and others--which are operable through relatively narrow diameter cannulas.
The general approach to developing such endoscopic instruments has been to adapt known, open-surgical-procedure instruments to endoscopic use by separating the handle portion of such instrument from the working elements by means of interposing an extended shaft. One well-accepted design of endoscopic instruments incorporates a pair of ring handles pivotably joined to each other and to the proximal end of an elongated support shaft which is secured to one of the ring handles. The other ring handle is operatively connected to an actuating rod which is aligned along the axis of the support shaft. Pivoting the ring handles about their pivot point produces a longitudinal motion of the actuating rod relative to the support shaft. By connecting various working elements to the distal ends of the support shaft and the actuating rod, the pivoting motion of the ring handles may be translated into pivoting motion of the working elements relative to each other at the distal tip of the endoscopic instrument. In the case of scissors, the working elements are a pair of scissor blades.
While this relatively straightforward way of adapting open-surgical-procedure instruments to endoscopic use is of some value for many types of instruments, there are some limitations which limit the acceptability of this approach for certain instruments. For example, the forces which are able to be transmitted from the ring handles of a pair of endoscopic scissors to the distal tip of the instrument via elongated actuating rods are constrained by certain design parameters. In conventional non-endoscopic scissors the forces applied to the blades by the ring handles (before they touch) are almost directly representative of the force on the handles because each handle has a blade associated with it, both being on opposite sides of a single shaft. In endoscopic scissors, however, the various linkages and elongated components tend to be elastic enough to stretch slightly such that squeezing of the ring handles to their fully closed position does not necessarily result in complete cutting because the distal tips of the scissor blades may be held open by tough tissue. In the case of conventional endoscopic scissors the ring handles are adjusted so that when they are squeezed together they contact each other when the scissor blades are fully aligned (i.e. closed) without crossing over each other. This adjustment is made without any tissue interposed between the blades. No greater force may be applied when the ring handles touch and, therefore, if tough tissue is interposed the scissor blades merely stay open causing an incomplete cut. There is a need for some means to apply greater cutting force to endoscopic scissors.
Merely adjusting the ring handles so the blades are aligned when the handles are separated and permitted to be squeezed more, is an obvious but insufficient solution. If this were done, further squeezing of the handles could cause further pivoting of the scissor blades such that their distal tips would pass each other. The crossing over of the distal tips of scissor blades is particularly undesirable in endoscopic applications since the crossed over blades will result in sharp and dangerous tips which may be inadvertently harmful to adjacent tissue at the endoscopic work site.
It is accordingly an object of this invention to produce a surgical instrument in which the application of force from the proximal end of the instrument to its distal tip is optimized.
It is a further object of this invention to provide a surgical instrument in which an actuating means at the proximal end of the instrument is able to apply force between a pair of working elements at the distal tip of the instrument even after the working elements have reached their fully closed position.
It is a further object of this invention to provide scissors for use in endoscopic surgical procedures wherein the scissors are provided with means to prevent their tips from crossing over.
It is another object of this invention to produce a pair of endoscopic scissors which is easier to adjust in manufacturing.